The present invention relates to a device for driving an objective lens of an optical disk. Particularly, the present invention relates to an objective lens driving device which can effectively drive an objective lens for collecting light onto a recording surface of an optical disk so as to move the objective lens in the focusing direction and the tracking direction, and relates to an optical disk drive using such an objective lens driving device.
Examples of background-art objective lens driving devices include those which are disclosed, for example, in JP-A-6-4885, JP-A-7-320278 and JP-A-8-297846.
In the objective lens driving device disclosed in JP-A-6-4885, a pair of magnets are disposed so that opposite magnetic poles are provided on the right and left while the same poles face each other, and extension portions of a yoke are provided between the same poles of the respective magnets which poles are facing each other, in order to keep the leakage of magnetic flux to a minimum.
In the objective lens driving device disclosed in JP-A-7-320278, plate-like magnetic substances each having a surface substantially perpendicular to the tracking direction are provided at the tracking-direction opposite ends of a fixed base in order to make the distribution of magnetic flux density uniform in the tracking direction in a magnetic air-gap portion to thereby prevent influence of leakage magnetic flux from a turn table or the like.
In the objective lens driving device disclosed in JP-A-8-297846, a yoke of a magnetic substance has a substantial U-shape so as to hold a permanent magnet and at least one of a focusing coil and a tracking coil between opposite portions of the yoke in order to make magnetic flux generated from the magnet interlink at right angles with a current flowing in the coil to thereby generate a thrust force for moving an objective lens effectively.
However, in such a background-art objective lens driving device, for example, in the configuration disclosed in JP-A-6-4885, the area of the yoke facing the magnets is small so that magnetic flux from the magnets cannot be kept at right angles to a coil. Therefore, the configuration is not always sufficient in a point that a thrust force for driving an objective lens is obtained effectively.
In the configuration disclosed in JP-A-7-320278, the plate-like magnetic substances are outside a focusing coil. Accordingly, the plate-like magnetic substances attract magnetic flux from a magnet in parallel with the tracking direction aggressively, so that a force opposite to an effective thrust force acts on the focusing coil. Therefore, also this configuration is not always sufficient for obtaining a thrust force for driving an objective lens effectively.
Further, in the configuration disclosed in JP-A-8-297846, an auxiliary yoke is outside the focusing coil. Accordingly, the auxiliary yoke attracts magnetic flux from a magnet in parallel with the tracking direction aggressively, so that a force opposite to an effective thrust force acts on the focusing coil. Therefore, also this configuration is not always sufficient for obtaining a thrust force for driving an objective lens effectively.